1. Field of the Invention
The present invention relates to a wafer support device and a component used for the wafer support device.
2. Description of the Related Art
Plasma CVD apparatuses, plasma etching apparatuses, and plasma ashing apparatuses are known examples of plasma processing apparatuses. In these plasma processing apparatuses, a wafer support device is generally used to place a wafer in a vacuum chamber. The wafer support device includes an electrostatic chuck provided to attract and fasten a wafer as an object of plasma processing and a cooling plate arranged to cool dozen the electrostatic chuck. The electrostatic chuck has an internal electrode embedded in an insulating material or a dielectric material (for example, a ceramic material). In the wafer support device, the wafer is placed on a wafer mount surface of the electrostatic chuck, and a direct-current voltage is applied to the internal electrode to generate an electrostatic force (Coulomb force or Johnson-Rahbek force) and thereby attract and fasten the wafer onto the wafer mount surface. In this state, the wafer is exposed to plasma, which is generated by application of a high-frequency voltage between an upper electrode located in the vacuum chamber and the internal electrode embedded in the electrostatic chuck or between the upper electrode and the cooling plate.
The generated plasma is used for processing the wafer but may also erode an area close to the wafer. When the wafer mount surface of the electrostatic chuck is greater in dimensions than the wafer, a marginal area of the wafer mount surface outside the wafer is directly exposed to the plasma and may thus be eroded. One measure against this potential problem makes the wafer mount surface of the electrostatic chuck smaller in dimensions than the wafer, forms a step lower than the wafer mount surface around the outer circumference of the wafer mount surface of the electrostatic chuck, and places a replaceable protection ring on the step. The protection ring works to stably expose the outer circumferential edge of the wafer to the plasma and protect the surface of the electrostatic chuck. The diameter of the wafer is greater than the diameter of the wafer mount surface of the electrostatic chuck. A top surface of the protection ring is formed to have a height lower than the wafer so that the outer circumferential edge of the wafer is accordingly protruded from the wafer mount surface. The outer circumferential edge of the wafer is not in contact with but is slightly away from the protection ring. During plasma processing of the wafer, the protection ring is naturally exposed to the plasma and has a temperature increase. In a wafer support device 220 of Patent Document 1 shown in FIG. 8, a coolant gas flow path 250 is provided to prevent an excessive temperature increase of a protection ring 230. The coolant gas flow path 250 is formed to pass through a step 26 of an electrostatic chuck 22 in a vertical direction. A flow of coolant gas (helium gas) is supplied through the coolant gas flow path 250 to cool down the protection ring 230. The electrostatic chuck 22 is cooled down by a cooling plate 40.
Patent Document 1: Japanese Patent Laid-Open No. 2005-64460